A bit line contact that connects a cell transistor of a DRAM (Dynamic Random Access Memory) and a bit line to each other is made of a doped polysilicon filled in a bit contact hole. The bit contact hole is an opening formed in a multilayered structure. When a non-doped polysilicon is used as a dielectric film including the multilayered structure, a dopant may diffuse from the doped polysilicon constituting the bit line contact to the non-doped polysilicon constituting the dielectric film including the multilayered structure. In this case, a part of the non-doped polysilicon changes to a doped polysilicon having some conductivity, which causes a problem that a bit line capacitance is increased. Furthermore, if the dopant diffuses, the dopant concentration in the doped polysilicon constituting the bit line contact is decreased and thus another problem occurs that the resistance value of the bit line contact is increased.